The present invention relates to magnetic resonance imaging (MRI), and in particular, to a laser apparatus for guiding surgical procedures based on location information derived from such MRI imaging.
MRI is a technique for imaging structures within a patient""s body. An atomic nucleus carries a charge and due to the intrinsic spin associated with the charged nucleus, each nucleus acts like a magnetic dipole. When an external magnetic field is applied to a patient""s body, the nuclear dipoles are forced into orientation to the external field. An applied radio frequency pulse at a resonance frequency tilts the nuclei out of alignment. After the pulse passes, the nuclei relax and emit an electromagnetic signal that can be detected by antennas. The detected signal is then analyzed by a Fourier transform technique to yield an image of the internal structure of the patient""s body. By manipulating the imposed external magnetic field and the applied radio frequency pulse, the image may be selected to be in a narrow plane. A sequence of such planes provides complete three dimensional information about the internal structure of the portion of the patient""s body being imaged. Images may be taken in the coronal plane (the plane that divides the structure into front and back portions), the axial plane (the plane that divides the structure into left and right portions), and the sagittal plane (the plane that divides the structure into upper and lower portions).
If the images of the patient""s body show a suspect mass, invasive surgical procedures including biopsy or ablation may be required. Localization of the suspect mass may be performed by the insertion of wires under the guidance of the MRI image. Various techniques are known for guiding an instrument to a suspect mass, e.g., mechanically aligned bores which guide the instrument from a selected entry point to the suspect mass. Such systems are called stereotactic, which means the use of vectors to position an instrument in three-dimensional space.
Such mechanical stereotactic systems are complicated and allow the surgeon little freedom in guiding the instrument. This is a severe limitation in that the skill of the surgeon is often required to precisely locate the suspect mass and insert the instrument into the mass. It is also desirable that a stereotactic system by constructed entirely of non-magnetic material, such as acrylic, aluminum or stainless steel since the system must operate within the fringes of the powerful MRI field. Finally, it is also desirable that a stereotactic system be lightweight, portable and adaptable to various types of MRI devices or to other types of imaging systems. Battery power, for example, would allow a stereotactic system to be independent of the power supply of the; imaging system.
The limitations of the prior art are overcome by the present invention as described below.
The present invention provides the radiologist performing biopsies and ablations of suspect masses localized by magnetic resonance imaging with a reference to guide needle or fiber insertion into the mass. The invention must be used within the fringe field of the MRI magnet and thus is non-magnetic to prevent the device from being torqued or drawn into the bore of the magnet. Part of the design criterion was that the invention be simple and inexpensive. The invention is able to be adapted to any type of patient table used for delivering a patient to the bore of a MRI magnet or other imaging device. The invention is battery operated and self contained, thus independent of any power requirements of the MRI system.
The stereotactic device of the present invention includes horizontal and vertical protractors on which a laser is mounted. The protractors and laser are mounted on a table which may be positioned horizontally and vertically with respect to the patient table. The portion of the patient""s body being imaged, for example, a breast, is fixed by a compression plate to which a reference target is mounted. The reference target incorporates a substance which is strongly imaged by the MRI. The compression plate comprises an array of relatively large apertures through which the radiologist may guide an instrument. It is an important aspect of the present invention that the apertures are not narrow bores limiting the freedom of movement of the instrument. The apertures provide access but are not guides.
From the MRI images, the radiologist takes an angle between the reference target and the suspect mass from each of two perpendicular planes and inputs these angles into the protractors of the stereotactic device which is mounted on the side of the MRI patient table. The table of the stereotactic device is then adjusted horizontally or vertically with respect to the patient table so that the beam of the laser aligns with the reference target. The reference target is then removed from the compression plate so that the laser beam illuminates an entry point on the patient""s body. The laser beam is thus aligned along a trajectory from the entry point to the suspect mass. The radiologist is then able to simply follow the laser beam with a biopsy needle or other instrument to make consistent arrival at the site of the suspect mass. The radiologist is able to target multiple pathways from the same entry site or multiple approaches to the target.
The stereotactic device of the present invention is independent of any particular MRI or other imaging system and thus no modifications to an existing system are required. It is desirable that the stereotactic invention be xe2x80x9cportablexe2x80x9d in the sense that it may be adapted to various types of imaging devices and in operation is independent of any particular imaging device. The invention may however be affixed in a permanent or semi-permanent fashion to a particular imaging device.
MRI images provide excellent localization of masses, but the information is not xe2x80x9creal time.xe2x80x9d Without a guidance system, the only way a radiologist can arrive at the suspect mass with needle insertion is through a hit-and-miss iterative process. The stereotactic device of the present invention provides guidance to the suspect mass and thus saves valuable time and multiple xe2x80x9csticksxe2x80x9d to the patient, while allowing the radiologist freedom to adjust the trajectory of the instrument as necessary.
The present invention has been designed for breast biopsies and laser ablation in breasts, but is not so limited and could be used for other areas such as liver or kidney.
The design of presently available MRI coils and the patient table may limit the field of view of the invention. However, these limitations may be overcome by redesigning the coil and patient table.
It is therefore an object of the present invention to provide for a stereotactic system which provides the radiologist performing biopsies and ablations of suspect masses localized by magnetic resonance imaging with a reference to guide instrument insertion into the mass while allowing the radiologist freedom in guiding the instrument.
It is a further object of the present invention to provide for a stereotactic system which is non-magnetic and operable in the fringe field of an MRI magnet.
It is also an object of the present invention to provide for a stereotactic system which is able to be adapted to any type of patient table used for delivering a patient to the bore of a MRI magnet or other imaging device.
It is an additional object of the present invention to provide for a stereotactic system which is battery operated and self contained, thus independent of any power requirements of the MRI or other imaging system.
These and other objects and advantages of the present invention will be apparent from a consideration of the following detailed description of the preferred embodiments in conjunction with the appended drawings as described following.